As the reality of climate change continues to jeopardize the livelihoods of people across the world, Sunday's show looks at global efforts for alternative energy sources. Scotland's two year effort to harness energy from gigantic tidal turbines off the northern coast, about 100 feet below water, has provided promising results. It may be the prelude to the world's largest tidal energy project, which will attempt to generate enough power for a quarter of a million households. Hari Sreenivasan visits the spectacular testing lab while asking the pressing question: could this work in the U.S.?